1. Field of the Invention
The present invention relates to an obstacle detecting device in which an ultrasonic sensor including an ultrasonic transducer is attached to a wall member and which sends and/or receives ultrasonic waves via the wall member.
2. Description of Related Art
Obstacle detecting devices are known which detect obstacles around a vehicle using an ultrasonic sensor, for example. For example, in the obstacle detecting device having an ultrasonic sensor that is disclosed in JP-A-2004-264264, a hole is formed in a bumper of a vehicle and the head portion of the ultrasonic sensor is exposed through the hole so as to be flush with the outer surface of the bumper. However, since the head portion of the ultrasonic sensor is exposed to outside the vehicle, the obstacle detecting device having such a structure is not preferable in terms of design.
For example, the obstacle detecting device of JP-A-10-123236 has been proposed as a countermeasure against the above disadvantage. That is, the design performance is improved by providing a recess on the back side of a bumper of a vehicle and housing an ultrasonic vibration type sensor in the recess so that the sensor is unseen from the outside.
Incidentally, in the obstacle detecting device of JP-A-10-123236, an ultrasonic sensor in which a disc-shaped ceramic member (ultrasonic transducer) is laid on a metal base so as to form an integral lamination member is attached to the bottom wall of a recess that is larger than the ceramic member in a plane that is parallel with the bumper in such a manner that the outer surface of the ceramic member is in direct contact with the bottom wall of the recess. Therefore, vibration (what is called unwanted vibration) tends to be transmitted to around the portion of the bumper that is in contact with the ultrasonic sensor (ceramic member), in which case vibration occurs in a wide range of the bumper to cause irregular directivity. This is considered due to a phenomenon that the wide-range vibration produces different phases at individual positions and thereby causes interference.